Hopes of tackling diseases such as malaria by creating genetically modified (GM) mosquitoes that resist parasite and viral infections have suffered a setback following new research confirming that such mosquitoes may be less able to survive than their normal counterparts.

The findings come from a study of the Aedes aegypti mosquito,which transmits yellow fever and dengue, published this month in the Proceedings of the National Academy of Sciences.

The researchers, led by Nic Irvin from the University of California, United States, analysed how well GM mosquitoes were able to survive and reproduce compared to normal laboratory mosquitoes.

They found that GM mosquitoes performed worse than their normal counterparts, indicating that GM mosquitoes would probably be poor competitors against naturally occurring strains of mosquito. This could hinder potential disease-control strategies that rely on releasing GM mosquitoes into the wild, as these depend on the GM strains being successful and spreading resistance to the disease throughout the population.

The results back up a study published last year on a different type of mosquito – Anopheles stephensi, which transmits malaria – that also suggested that GM mosquitoes were less well able to survive than their normal counterparts (see GM mosquitoes not fit enough).

According to Anthony James, a specialist in GM insect vectors at the University of California at Irvine, United States, however, the findings do not mean that GM mosquitoes cannot be used to combat human diseases.

“I do not see findings that transgenic insects are less fit than laboratory or wild-type mosquitoes to be a major challenge to the use of transgenics to control disease transmission,” he says. “I take it as a given that any [gene] inserted into the genome of a mosquito would [reduce the changes of survival of] that mosquito.”

He says that the study provides a good set of parameters by which to measure how well different types of GM mosquitoes can survive and reproduce. "Having these measurements will help in comparing different strains of genes,” he adds.